In prior art there is known a radial piston hydraulic motor design in which a cam ring is connected to a box frame. The cam ring is a wave-shaped structure, and pistons connected to a non-revolving piston frame can be pressed one after another against the inner surface of the wave-shaped structure. Some of the pistons are in a working phase and some of them in a return phase. The supply of oil into the piston frame is regulated through a distributor valve, which revolves with the box frame. The piston frame is connected with the central non-revolving central shaft.
From the prior art designs, separate neutral position valves are known through which the motor can be disengaged to be in a neutral state so that the box frame and a structure associated therewith, for example, a wheel of a vehicle, can be rotated freely. The neutral position valves in accordance with the prior art are component units which are outside the structure and which, with their extra hoses and connections, increase the price of the system and slow down installation.